Multifunction portable devices ideally provide a user with maximum flexibility and capability in a single compact and portable package. Such devices may be based on devices such as portable telephones and personal digital assistants (PDAs) that are enhanced to provide capabilities beyond communications or computing. Image capture functions, for example, are a desirable addition to the capabilities of such devices, and compact CMOS image sensors are now making possible the cost-effective addition of image capture capabilities to portable devices such as telephones and PDAs.
The image sensors in portable devices are preferably inexpensive and must necessarily be small to minimize the size of the portable device. These restrictions on the image sensors generally require that the image sensors have a lower image resolution than would be used in a state of the art digital camera. A current digital camera, for example, may provide megapixel resolution for images, while an image sensor that is practical for a telephone or PDA may only provide a CIF or VGA resolution (i.e., 352×288 or 640×480).
The lower resolution of a small and inexpensive image sensor is adequate or even preferable for many uses of imaging in multifunction portable devices. Low-resolution image sensors, for example, often provide greater sensitivity and greater dynamic range because of the acceptability of larger pixel size. Further, images having a lower resolution require less memory for storage and less bandwidth for transmission, which is important for a portable device having a relatively limited amount of available memory and/or transmission bandwidth. A low resolution image sensor may also match the resolution of a viewfinder or other small display on the portable device allowing direct display the low-resolution images from the low-resolution image sensor without up or down sampling that consumes processing power.
On some occasions, users will want to capture images at a higher resolution or quality than the image sensor in a multi-function device can provide. Such users currently need to have a separate camera or other device for high-resolution imaging. A method for providing high-resolution images using a low-resolution image sensor is thus needed to permit a multi-function portable device to serve more imaging functions.